Heat-transfer fluids are used as heat carriers in many applications, particularly as coolants or antifreeze. Examples of use of heat-transfer fluids include the removal or exchange of excess heat from stationary and automotive internal combustion engines, heat generated by electrical motors and generators, process heat and condensation heat (e.g. in refineries and steam generation plants), electronic equipment or fuel cell systems. In all of these applications the thermal conductivity and heat capacity of the heat-transfer fluid are important parameters in the development of energy-efficient heat-transfer equipment. To improve the total efficiency of their equipment, industries have a strong need to develop heat-transfer fluids with significantly higher thermal conductivities than presently available.
Historically, water has been the preferred fluid when considering heat transfer. In many applications, antifreeze properties are needed and the water is mixed with freezing point depressants like alcohols, glycols or salts. Such mixtures do have a decreased heat transfer capability in comparison with pure water but are still preferred above liquids like organic oil, silicone oil or synthetic esters.
Certainly in the cooling of an internal-combustion engine, motors and the like, heat transfer mediums for hot-water supply, heating, cooling and freezing systems, heat transfer mediums for a snow melting system, road heating, industrial cooling installations, power generation systems and even fuel cell and battery cooling, aqueous solutions are still the preferred option from a heat transfer perspective.
The heat exchange property of heat transfer mediums is controlled by the specific heat, density, viscosity and thermal conductivity of its base fluids. These heat transfer parameters are, to a limited extent, impacted by the addition of minor amount of the normal additives like corrosion inhibitors, scale inhibitors, stabilizers, antioxidant, buffers, de-foamers, and dyes. Although its use dominates the engine coolant market, water/glycol mixtures and even pure aqueous solutions do not always give sufficient heat transfer performance in high demanding system where the thermal load has reached its limit.